Protective circuit



June 17, 1958 W. H. BAUMGARTNER EI'AL Klbu K2 Kl KlGa.

R Am mm Y M CNL VWS R NU w B0 m A Mm AA IH Mm wR Y B PROTECTIVE CIRCUITWilliam H. Baumgartner, Glenside, and Richard C. Weise, Philadelphia,Pa., assiguors to Burroughs Corporation, Detroit, Mich., a corporationof Michigan Application October 27, 1955, Serial No. 543,138

2 Claims. (CI. 317-9) The present invention relates to power supplycontrol systems and more particularly to an associated circuit forprotecting electronic systems, such as electronic computers, from damageor inaccurate operation from re duced supply potentials.

In such systems and particularly those involving a multiplicity ofrelays, switches and the like, a blown ruse, a short circuit or someother circuit interruption leaves the general circuit assembly open todamage by someone attempting to restart the equipment without callingupon maintenance service to properly check restored circuits.

An object of the invention is to provide a protecting system for powersupplied circuits of an electrical apparatus;

Another object is to provide means to prevent repaired or restored powercircuits from being turned on by present conventional means;

A further object applies specifically to the replacement of blown fusesby an operator of an electronic computer to prevent such operator fromrestarting the. equipment without proper rechecking by qualifiedpersonnel;

A still further object is to provide novel means for starting or closinga circuit after failure of power to an electrical system; and 1 Toprovide other improvements as will hereinafter appear.

In the accompanying drawings Fig. l representsa control circuit for apower supply system equipped with a protective system embodying one formof the invention and showing the initial relation of the circuitelements with the voltage supply line open;

Fig. 2 represents the same circuit in operated condition with thevoltage supply line closed;

Fig. 3 represents an illustrative power supply circuit to which theprotective circuit is responsive in case of a power circuit failure, and

Fig. 4 is a detailed circuit diagram of a typical set of protectivecontacts used in the system with the power supply circuit of Fig. 3.

Referring to the drawings, and particularly to Fig. 1, the lineconductors and 11 of the circuit are supplied from a source of voltagethrough a control switch 8-3 which when closed starts the power controlcycle by energizing relay K2 through closed contacts K16a and K3a toclose the circuit for the D. C. power supply of Fig. 3. The solenoid ofrelay K2 is in series with relay contacts Kla which remain normallyclosed and relay contacts K3a which are replaced in operation with therelay contacts Ks as shown in Fig. 4 when normal voltages exist in thecircuit of Fig. 3. The contact K311 thus is in parallel with thenormally open relay contact Ks, which is a series of any suitable numberof sensing relay contacts such as used in power supply circuits forcomputers or other equipment as illustratively shown in Fig. 4. Thusthere are two circuit controlled paths one by way of contacts K16a andK3a and the other by way of United States "ice contacts K16a and Ks, theformer two functioning for the initial closing of the D. C. power andthe latter two maintaining a closed path upon operation of the powersupply energization cycle. The relay contacts K16a are included in theprotective circuit of the invention as will be explained, and thus areonly opened after a failure of power when the energization cycle hasbeen completed.

For operating the contacts K16a to break the line circuit through therelay K2, when trouble develops in the output circuit of relays K6 to K9of Fig. 3, a latching relay K16 is provided, which is normallyde-energized to hold contact K1611 closed when either one or both rclaycontacts K14a and K15a are open. Latching relay K16, which holdscontacts K16a open when latched, is in line series relation with therelay contact K and KlSa, respectively open and closed at the initialconditions of Fig. 1. Initially, the open relay contact K14a is arrangedto be closed by its time delay relay K14 to lead line voltage to relayK3 for opening relay Contact K3a after the power supply of Fig. 3operates to close relay contacts Ks. Contact K15a is opened by relay K15in parallel with relay K2, thereby serving to open the circuit to relayK16 whenever relay K2 is energized and to prevent operation of relay K16whose contact K16a with either contact K3a or Ks maintains the powersupply in operation. Thus, as long as conditions are normal in thecircuit of Ks after the power is on, the relay K16 remains tie-energizedand in unlatched condition. When the output circuit is interrupted bysome abnormal condition such as shorting of leads 12, or opening of fuse13 to open one of the Ks contacts, the relay K16 becomes energized andbecomes automatically latched in open position to prevent improperrestoring of any of the circuits until the trouble has been corrected. Arelease coil R10 is provided in an auxiliary line circuit 20 undercontrol of a push button switch 23 or the like for manual operation.Preferably in practical use the switch 23 is under the control panel andoperated by a key only available to an authorized serviceman, as anadditional safeguard against restoring the circuits.

The general operation of the control cycle is described in connectionwith both Figs. 1 and 2. With switch S3 closed, the line voltage causesthe relay K2 and K15 to 'close through the normally closed contacts K16aand K3a, as shown in Fi 1, while simultaneously the time delay relay K14starts in operation. Due to this delay, the contact K1412 is still openand relay K3 is held in its deenergized state so that the relay K16remains deenergized even though contact KlEa is closed at the instantthe switch S3 is closed. The line voltage through K2, contact K16a andK3zz energizes the D. C. power supply of Fig. 3, while at the same timethe relay K15 opens contact K15a allowing K16 to remain de-energizedeven after the pro-determined delay interval of K14 permits the contactK1412 to close, whereupon relay K3 opens contact K3a and passes controlto the series contacts Ks. However, since the various voltages of the D.C. power supply are now up to value, all of the sensing relays K6 to K9are energized to thereby close contacts K6a to K911 of Ks and allowingthe circuit through relays K2 and K15 to remain complete. The circuitsare now as shown in Fig. 2 and so remain as long as all power outputcircuits are closed and functioning properly.

Now in case of circuit failure in which one or more of the D. C.voltages is reduced sufiiciently, due to a blown fuse or other cause, toopen the corresponding sensing relay K6 to K9, thereby causing ContactKs to open whereby relays K2 and K15 drop out. The dropping out of K2turns oh? the D. C. power supply, while the dropping out of K15 causesthe contact K15a to return to its normally closed position. Since switch8-3 is closed, contact K14a is still closed and the closing of tact K2.

contact Ka energizes and latches the relay K16 and consequently opensthe contact K16a which is in series with the coil of K2 therebypreventing restoration of the D. C. supply. Since the relay K16 islatched the circuits controlled by it must remain open until the switch8-5 is closed to energize the release coil R40 and restore conditions sothat K2 can operate to turnon the D. C. power supply again. As long asthe relay K16 is latched the relay K2 cannot function even though theswitch S3 be opened and then closed. 7

In Fig. 3 of the drawings one form of electrical system is illustrativeof the type with which the circuit of the invention is associated, andas shown includes a plurality of power circuits to which the initiatingcircuit is connected and supplies power thereto by way of relay con-This system includes a plurality of sensing relays having seriesconnected contacts K6, K7, K8 and K9 as shown in Fig. 4, whereby theoutput contact Ks is opened by the failure of any of the relays K6 toK9. A type of power supply circuit shown in Fig. 3 is described andclaimed in the co-pending application of Richard C. Weise, Serial No.595,884, filed July 5, 1956, and assigned to the same assignee as thepresent application.

In a computer circuit designed for halting after an error is detected,the push button 21 and relay 22 may be used for re-starting the machinewhenever the error is not due to the failure of a power supply potentialwhich would open one of the contacts Ks.

What is claimed is: a

1. A protective circuit for electrical apparatus, said protectivecircuit comprising: a pair of leads energizable by a source voltage;first, second and third branch circuits connected in parallel betweensaid leads, said first branch circuit comprising the winding of a firstrelay in series with the normally-closed contacts of a second relay andin further series with the normally-closed contacts of a third relay,said first branch circuit also including, in shunt with the first-relaywinding, the winding of a fourth relay, said first branch circuit alsoincluding, in shunt with said third-relay contacts, the normally-opencontacts of a plurality of sensing relays, said sensing-relay contactsbeing connected in series, said first relay having normally-opencontacts which when closed connect a power supply to said apparatus, thewindings of said sensing relays being parallel connected to pass currenttherethrough in response to said power supply being connected to saidapparatus, said second branch circuit comprising the winding of atime-delay relay whose'actuation in response to said source voltagelagsbehind that of said sensing relays in response to said power supply,said third branch circuit comprising the normally-open contacts of saidtime-delay relay in series with the winding of said third relay, saidthird branch circuit also including, in shunt with said third-relaywinding, the normallyclosed contacts of said fourth relay seriallyconnected to the winding of said second relay, said second relay beingof a type which when energized latches in open-contact position; andmeans for unlatching said second-relay contacts, said unlatching meanscomprising a release winding on said second relay separately energizableunder the control of a separate control switch.

2. In a power supply system, a protective circuit comprising: a pair ofleads energizable from a source of voltage; a first switch forconnecting said leads to said source; a first circuit connected betweensaid leads, said first circuit including means responsive to saidvoltage on said leads for energizing a second switch to connect a powersupply to the apparatus to be protected; anormally-closed series elementincluded in said first circuit; a second circuit connected between saidleads, said second circuit including means which, in response to saidvolt age on said leads and after a delay, opens said series element insaid first circuit; sensing means included in said apparatus to beprotected which in response to said power supply provides a shunt patharound said first-circuit series element, said sensing means operating,in response to a power failure in said apparatus, to open said shuntpath; a third circuit connected between said leads, said third circuitincluding the winding of a latching relay whose contacts are seriallyincluded in said first circuit, said latching-relay contacts beingnormally closed when said latching relay is in tie-energized condition;means included in said third circuit which in response to current flowthrough said first circuit prevent the energization of said latchingrelay when said leads are connected to said voltage source; and means,including a release coil on said latching relay separately energizableunder control of a third switch, for unlatching said latching relay toreturn said first circuit to closed-circuit condition.

References Cited in the file of this patent UNITED STATES PATENTS1,312,454 Raney Aug. 5, 1919

